Compared with a peak rate of Long Term Evolution (LTE) system, a peak rate of LTE Advanced (LTE-A) system is improved greatly. A downlink rate and uplink rate of LTE-A system is required to be up to 1 Gbps and 500 Mbps respectively. Further, the LTE-A system is also required to be compatible with the LTE system. In order to improve the peak rate, enable the LTE-A system to be compatible with the LTE system and take full advantage of frequency resources, a Carrier Aggregation (CA) technology is introduced into the LTE-A system.
By the CA technology, multiple cells may be aggregated by a User Equipment (UE) at the same time. The UE may be a terminal device. These cells may belong to the same band. In this case, the CA technology is called an intra-band CA technology. These cells may also belong to different bands. In this case, the CA technology is called an inter-band CA technology. No matter whether these cells belong to the same band, as long as the capability of the UE can support the aggregation of these cells, these cells may provide a data transmission service for the UE at the same time. In order to enable the LTE-A system to be compatible with the LTE system, the maximum bandwidth of each cell may be 20 MHz, and bandwidth between member carriers may be the same or different.
Time Alignment (TA) mechanism may ensure that uplink signals of all cells aggregated by a UE reach a base station at the same time to avoid interference. For the UE, non-synchronous uplink data transmission should be avoided.
LTE-A R10 only supports a single-TA scenario, in which TAs of all cells aggregated by the UE are the same.
A multi-TA scenario is introduced into LTE-A R11, in which TAs of all cells aggregated by the UE may be different. The multi-TA scenario may be an inter-band CA scenario or an intra-band CA scenario. In the intra-band CA scenario, data transmission of partial cells belonging to this band passes through a Remote Radio Head (RRH) or a repeater.
Several multi-TA scenarios that have been defined by 3rd Generation Partnership Project (3GPP) are described as follows.
In scenario 1, as shown in FIG. 1, the UE aggregates F1 and F2, the coverage of F1 is smaller than the coverage of F2, and F1 and F2 belong to different bands. That is, the scenario 1 is the inter-band CA scenario.
In scenario 2, as shown in FIG. 2, the UE aggregates F1 and F2, and F1 and F2 belong to different bands. That is, the scenario 2 is the inter-band CA scenario.
In scenario 3a, as shown in FIG. 3, the UE aggregates F1 and F2, F1 and F2 belong to the same band, but F2 passes through a repeater. That is, the scenario 3a is the intra-band CA scenario, but data transmission of partial cells passes through a repeater.
In scenario 3b, as shown in FIG. 3, the UE aggregates F1 and F2, F1 and F2 belong to different bands, and F2 passes through a repeater. That is, the scenario 3b is the inter-band CA scenario, and data transmission of partial cells passes through a repeater.
In scenario 4a, as shown in FIG. 4, the UE aggregates F1 and F2, F1 and F2 belong to the same band, but F2 passes through a repeater. That is, the scenario 4a is the intra-band CA scenario, but data transmission of partial cells passes through a RRH.
In scenario 4b, as shown in FIG. 4, the UE aggregates F1 and F2, F1 and F2 belong to different bands, and F2 passes through a repeater. That is, the scenario 4b is the inter-band CA scenario, but data transmission of partial cells passes through a RRH.
In order to maintain TAs in a multi-TA system, a concept of TA group is introduced. Uplink Component Carriers (UL CCs) of cells belonging to one TA group may use the same TA value, and UL CCs of cells belonging to different TA groups use different TA values. As long as the UE keeps uplink synchronization with one cell in a TA group, the UE may keep uplink synchronization with all cells in the TA group.
A TA group including a Primary Cell (PCell) may be called a PCell TA group (PTAG), and a TA group including a Secondary Cell (SCell) may be called a SCell TA group (STAG).
After the UE accesses a network, the network may query the capability of the UE. After receiving a capability querying request from the network, the UE reports the capability of the UE to a base station.
A signaling process of reporting the capability of the UE is shown in FIG. 5.
Based on the capability of UE in LTE R8/9, some new capabilities may be added to a UE in LTE-A R10 through non Critical Extension. The new capability may include a UE-category capability, a Radio Frequency (RF) capability, a measurement capability, an incontinuous resources assigning capability and so on. The Radio Frequency (RF) capability provides all BandCombination that may be aggregated by the UE.
A BandCombination Information Element (IE) includes two parameters, CABandwidthClass and a Multiple-Input Multiple-Output (MIMO) capability. CABandwidthClass defines the number of CCs that may be aggregated by the UE, as shown in Table 1.
TABLE 1The definition of CABandwidthClassaggregated transmission bandwidth(denoted with Physical Resourcethe number ofCABandwidthClassBlock (PRB))supported CCsAN <= 1001BN <= 1002C100 < N <= 2002D200 < N <= 300undeterminedE300 < N <= 400undeterminedF400 < N <= 500undetermined
In LTE-A R10, because only intra-band aggregation is supported in uplink, the aggregated cells indicated in the BandCombination all belong to this band.
The inventors find following problems in the prior art.
According to the multi-TA scenarios defined by 3GPP, multiple TAs should be considered in LTE-A R11, but a capability of supporting multiple TAs is not needed for the UE in LTE-A R11. And thus, it is required to consider how the UE reports to a base station information indicating whether the UE supports a multi-TA capability.